Hementin is an

anticoagulant Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where the ...

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

(fibrinogen lytic enzyme) from the

salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary gla ...

s of the giant

Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...

leech Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodie ...

(''

Haementeria ghilianii ''Haementeria ghilianii'', the giant Amazon leech, is one of the world's largest species of leeches. It can grow to 450 mm (17.7 in) in length and 100 mm (3.9 in) in width. As adults, these leeches are a greyish-brown colour, ...

''). Hementin is a calcium-dependent protease with a molecular weight of 80-120 kDa, and it contains 39 amino acid sequences. Hementin is present in both the anterior and posterior salivary glands, however it is mostly produced from certain cells in the anterior glands. The secretion of hementin is limited to the lumen of the

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...

, which the Amazon leech inserts into the host to suck blood. Hementin dissolves

platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...

-rich blood clots and lets the blood flow through the proboscis. Hementin is able to dissolve a type of blood clots that cannot be dissolved by other compounds, such as

streptokinase Streptokinase (SK) is a thrombolytic medication activating plasminogen by nonenzymatic mechanism. As a medication it is used to break down clots in some cases of myocardial infarction (heart attack), pulmonary embolism, and arterial thromboemboli ...

and

urokinase Urokinase, also known as urokinase-type plasminogen activator (uPA), is a serine protease present in humans and other animals. The human urokinase protein was discovered, but not named, by McFarlane and Pilling in 1947. Urokinase was originally i ...

. The processes of blood anticoagulation by hementin includes the degradation of fibrinogen. It is capable of disrupting the function of

fibrinogen Fibrinogen (factor I) is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood clo ...

, a glycoprotein responsible for blood clotting, by cleaving three peptide bonds in its structure. Hementin is also capable of segregating platelets by cleaving the fibrinogen cross-link amongst the platelets. Fibrinogen acts as a substrate for

thrombin Thrombin (, ''fibrinogenase'', ''thrombase'', ''thrombofort'', ''topical'', ''thrombin-C'', ''tropostasin'', ''activated blood-coagulation factor II'', ''blood-coagulation factor IIa'', ''factor IIa'', ''E thrombin'', ''beta-thrombin'', ''gamma- ...

, which converts this protein into its functional form,

fibrin Fibrin (also called Factor Ia) is a fibrous, non-globular protein involved in the clotting of blood. It is formed by the action of the protease thrombin on fibrinogen, which causes it to polymerize. The polymerized fibrin, together with platele ...

. Cleavage of fibrinogen in its native conformation at AαAsn102-Asn103, BβLys130-Gln131, and ϓPro76-Asn77 yield three sets of products. Hementin may also cause platelet deaggregation, although not under all circumstances. Because of its anticoagulant effects, Hementin can be described as a hemostatic regulator.

References

External links

* {{cite journal , last1=Malinconico , first1=SM , last2=Katz , first2=JB , last3=Budzynski , first3=AZ , title=Hementin: anticoagulant protease from the salivary gland of the leech Haementeria ghilianii. , journal=The Journal of Laboratory and Clinical Medicine , date=January 1984 , volume=103 , issue=1 , pages=44–58 , pmid=6361187 Anticoagulants